This invention relates to a method of controlling the fuel supply to an internal combustion engine by means of an electronic fuel supply control system, and more particularly to a method of this kind, which is adapted to increase the fuel supply quantity in response to the magnitude of change of the rotational speed of the engine after termination of a fuel cut operation.
In conventional methods of controlling the fuel supply to an internal combustion engine in response to operating conditions of the engine by means of an electronic fuel supply control system, it is generally employed to cut off the fuel supply to the engine at deceleration for improvement of the fuel consumption and emission characteristics of the engine, and then increase the quantity of fuel being supplied to the engine immediately after termination of the fuel cut operation, so as to improve the driveability of the engine. As such after-fuel cut fuel control methods, it has been proposed by Japanese Utility Model Provisional Publication No. 53-33721 to increase the fuel quantity by setting a longer fuel injection period for a predetermined period of time starting from the termination of a fuel cut operation, and it has also been proposed by Japanese Patent Provisional Publication No. 56-47631 to increase the fuel quantity by an amount corresponding to the duration of the immediately preceding fuel cut operation.
However, even if a fuel increase is effected immediately after a fuel cut operation according to the above proposed methods, the engine speed can suddenly drop to cause engine stall, when power transmission means such as the clutch of the engine becomes disengaged to interrupt power transmission from the engine to the vehicle wheels, through the driver's operation, immediately after the termination of the fuel cut operation. Further, if the fuel increasing quantity or increment applied immediately after termination of a fuel cut operation is set to a large value enough to avoid such engine stall, the resulting fuel supply quantity can be excessive if the power transmission means remains engaged and accordingly the magnitude of change of the rotational speed of the engine is small after termination of the fuel cut operation, which causes not only increased fuel consumption and deteriorated emission characteristics of the engine but also an acceleration shock upon transition from the fuel cut operation to a normal operation wherein fuel supply is effected.